Antimicrobial (algae) protection?

EK Water Blocks recommends the following steps be taken in order to prevent any biological growth within the warm waters of your computer liquid cooling loop:

Clean and rinse previously used water cooling equipment before using it.

Never use distilled water alone as your main coolant! Pure distilled water offers no protection against biological growth or corrosion.

Always use market proven pre-mix coolant, such as EK-Ekoolant. This propylene glycol based coolant contains all the necessary biological inhibitors, acts as a surfactant and also offers lubricating properties which enhance the lifespan of the water pump. Besides this, it also offers corrosion protection when used in a mixed-metal liquid cooling loop.

Refrain from using strips of Silver (Ag), also known as “Kill Coil”, with distilled water alone in your water cooling loop. Besides introducing another metal into the already mixed-metal loop with no corrosion protection, the concentration of Silver ions may not be enough to prevent or to suppress biological growth in the liquid cooling loop.

Refrain from using Copper (II) Sulphate (CuSO4) additive – common trade name “Nuke Cu” or “Biocide Cu” – due to its tendency to react with metals usually found in the liquid cooling loop, especially radiators (Zn, Cu, Sn) as well as Aluminum (Al) thus promoting corrosion. Using CuSO4 also accelerates visually discouraging copper tarnishing phenomena.

Always clean, rinse and dry water cooling equipment prior to storing it for later use!

The photo above shows the nickel-plated copper base of a poorly-maintained water cooling product.
Brown biological growth is clearly visible, as well as traces of plasticizer caused ‘gunk’ (source: overclock.net)

To sum it up: EK Water Blocks strongly advises against using any solution other than the market proven and tested pre-mix coolant. Using cheaper alternatives such as strips of Silver, Copper (II) Sulphate or some other homebrew solution with your expensive water cooling gear is just not even worth considering.